1. Field of the Invention
The present invention relates generally to automatic or semi-automatic firearms that incorporate a firearm barrel having a bore and having a cartridge chamber machined or otherwise formed within the barrel and being in communication with the bore. More particularly, the present invention concerns a cartridge chamber of a firearm barrel having internal wall treatment that facilitates the need for minimal extraction force during extraction of cartridge cases following the firing of cartridges. Even more specifically, the present invention concerns a method or process for generating an internal cartridge chamber surface that significantly reduces the surface contact area of the external tapered body surface of a cartridge case with the internal tapered surface of the cartridge chamber as compared with standard cartridge chambers. This invention also concerns cartridge chamber preparation for firearm barrels that ensure enhanced service life of the cartridge extractor and bolt mechanism of automatic and semi-automatic firearms.
2. Description of the Prior Art
The problem of cartridge case sticking has existed since about 1903 when ammunition having metal cartridge cases was initially developed for use in early machine guns. This problem has continued to plague the various manufacturers and users of firearms such as automatic and semi-automatic rifles, machine guns, artillery pieces, shotguns, in fact virtually every type of firearm that employs ammunition having a case that may be composed of metal, paper, polymer or a composite of various materials and is received within a chamber having a matching internal geometry with the external geometry of the cartridge case or shell case. The present invention is discussed herein particularly as it relates to small arms, such as rifles, machine guns and the like, but it is not intended to limit the spirit and scope of the present invention solely to these specific types of firearms, since the invention is readily applicable to a wide range of firearms and types of ammunition.
Most cartridge chambers are sized, relative to the cartridge case of the round to be fired, such that the cartridge can be easily inserted into the chamber. However, the fit of the cartridge case within the cartridge chamber must ensure that the cartridge case is maintained at a precise position in axial alignment with the bore of the barrel to ensure accuracy of firing. When a cartridge is discharged, such as by igniting gun powder within the cartridge case by striking a primer of the cartridge with a firing pin of a firearm, the rapidly burning gun power instantly generates high pressure within the cartridge case. This high pressure, which can be in the order of 50,000 psi or greater, ejects the bullet or other type of round from the neck of the cartridge case and propels it through the bore of the barrel toward the muzzle end of the firearm barrel. As a bullet is propelled by the substantially instantaneous high pressure of the cartridge gas, the high gas pressure acts rearwardly and instantaneously on the cartridge case, tending to drive the cartridge case and the bolt member rearwardly. This sudden rearwardly directed gas pressure induced force causes the bolt and extractor of a firearm to be subjected to significant instantaneous stress, which can cause premature failure of the bolt and/or extractor. The cartridge case, having been expanded by gas pressure to a tight fit within the cartridge chamber, tends to stick and resists initial rearward movement by the extractor, thus subjecting the extractor to significant instantaneous stress. When the cartridge gas pressure dissipates, the elastic memory of the cartridge case material will retract the cartridge case from its tight fit within the cartridge chamber, minimizing the extraction force that is necessary to extract the cartridge case of the spent cartridge from the cartridge chamber. Therefore, it is desirable to provide the cartridge chamber of a firearm barrel with internal surface preparation that develops controlled impedance to cartridge case extraction movement from the cartridge chamber and ensures the extended service life of both the extractor and bolt mechanisms of automatic and semi-automatic firearms. The controlled impedance is accomplished by minimizing the surface area contact of the external surface area of a cartridge case with the internal surface area of a cartridge chamber. This feature minimizes the gripping or frictional resistance of the internal spiral lands that compose a part of the internal surface geometry of the cartridge chamber with the external surface of a cartridge case. The degree of impedance is controlled by the dimensions of the internal spiral lands and by the geometry and orientation of the spiral lands and relief areas within the cartridge chamber.
The high pressure of gun powder combustion within the cartridge case causes expansion of the cartridge case and also causes minimal expansion of that portion of the firearm barrel that surrounds the cartridge chamber. The cartridge case, being composed of a yieldable material such as relatively thin brass, relatively thin steel, paper, polymer or various composites is deformed by the high internal pressure of cartridge gas so that it is urged outwardly and into relatively tight fitting relation with the internal surface of the cartridge chamber when the round is fired. When the cartridge case is in this pressure expanded tight fitting condition within the cartridge chamber it essentially establishes a friction resistance or gripping relation with the internal wall surface of the cartridge chamber. If, at this point, the extractor mechanism of the firearm should apply an extracting force to the pressure expanded cartridge case, the gripping relation of the cartridge case with the internal wall surface of the cartridge chamber will likely retard its extraction or will require a large extraction force to overcome this wall gripping relation and permit the extractor to begin extracting the cartridge case from the chamber. This large extraction force causes accelerated stress induced wear of the extractor mechanism and often results in breakage of the extractor, thus rendering the firearm inoperative.
In some cases the large extraction force will cause the cartridge case gripping portion of the extractor to yield the typically soft metal of the cartridge case and pull through its rearmost rim. Obviously, this condition leaves the stuck cartridge case within the chamber and requires the firearm user to insert a cleaning rod or similar implement through the bore of the barrel and push the cartridge case from the chamber. Efficient cartridge case extraction and ejection is necessary for virtually all automatic and semi-automatic firearms, and since these types of firearms are widely used by military and law enforcement personnel, a firearm that is rendered inoperative because of cartridge case extraction problems can subject the user to a dangerous condition. Moreover, tactical firearms must have the capability for operating efficiently over a wide temperature range and a wide variety of field conditions while experiencing minimal problems from the standpoint of cartridge case extraction and ejection.
The high pressure condition within the cartridge case will begin to be depleted as the bullet or other charge is propelled through the barrel bore and becomes depleted rapidly when the bullet leaves the muzzle of the barrel. When this occurs the minimally expanded portion of the barrel will rapidly return to its original condition and the cartridge case will begin returning from a pressure expanded condition substantially to its normal condition or geometry. After the cartridge case has become sufficiently contracted to diminish the gripping relation between the cartridge case and the cartridge chamber wall the cartridge case will be in a condition for easy extraction.
When used in automatic and semi-automatic firearms such as machine guns and tactical rifles, it is appropriate for the firearm mechanism to fire a round, extract and eject the spent cartridge case, and to charge the cartridge chamber with a fresh cartridge in the shortest possible period of time. Often, the timing of this process causes the extractor of the firearm to be applying significant pulling or extracting force on the spent cartridge case before contraction of the expanded cartridge case has progressed sufficiently to sufficiently diminish the frictional resistance and permit the cartridge case to be extracted by normal extraction force. This condition often causes excessive wear or mechanical failure of the extractor or causes the extractor to pull through the rim of the cartridge case. Therefore, it is desirable to provide for ease of extraction of cartridge cases even under conditions where the pressure expanded cartridge case has not yet returned to its retracted or relaxed state as cartridge gas pressure is being depleted.
Attempts were made many years ago to achieve substantially balanced gas pressure internally and externally of a spent cartridge case by fluting, i.e., internal longitudinal grooves that extend to the forward most end of the cartridge chamber. Fluting within a cartridge chamber permits gas pressure to be channeled within the cartridge chamber and externally of a spent cartridge case to provide a pressure balancing feature. Fluting permits the presence of cartridge gas pressure both internally and externally of the spent cartridge case causing the cartridge case to contract more quickly so that it may be extracted more easily. Channeling of cartridge gas pressure around the forward end of the cartridge case causes the differential pressure across the wall of the cartridge case to become substantially balanced. This pressure balancing activity quickly reduces the gripping relation of the spent cartridge case with the internal wall surface of the cartridge chamber and permits ease of cartridge case extraction. Examples of fluted cartridge chambers to promote gas pressure balancing are indicated by U.S. Pat. No. 2,383,356 of Wilson, U.S. Pat. No. 2,464,323 of Lee, U.S. Pat. No. 4,066,000 of Rostoeil and U.S. Pat. No. 5,479,737 of Osborne et al
When a round is fired by a firearm having a fluted cartridge chamber internal gas pressure will quickly expand the cartridge case against the internal wall surfaces of the cartridge chamber. As soon as the bullet of the cartridge is ejected from the cartridge case by the pressure expansion of gun powder ignition, gas pressure will enter the longitudinal flutes of the cartridge chamber and flow externally of the cartridge case, between the external surface of the cartridge case and the internal cartridge support wall surface of the cartridge chamber, toward the rearmost portion of the cartridge case. This external pressure counteracts the pressure within the cartridge case and minimizes the pressure differential that would otherwise exist across the wall of the cartridge case, thus establishing substantial pressure balancing and minimize the friction or gripping force that would otherwise prevent or delay cartridge case extraction from the cartridge chamber. This pressure balancing activity minimizes the period of time during which the cartridge case will be sufficiently expanded to have an extraction resisting gripping relation with the internal surface of the cartridge chamber and promotes rapid firing activity. However, this rapid firing capability is gained at the cost of fouling the cartridge chamber with gun powder residue and potentially damaging the cartridge cases.
A primary disadvantage of the fluted chamber method for balancing cartridge gas pressure is that a substantial amount of gun powder debris is typically generated during burning of the gun powder. A substantial amount of this cartridge gas debris is transported into the fluting grooves of the cartridge chamber externally of the cartridge case and constitutes fouling material which, if not removed by thorough cleaning, will build up in the cartridge chamber to the point that the firearm will have difficulty functioning and may cease to function normally.
Many firearm users regularly re-load their ammunition by recovering spent cartridge cases, subjecting the cartridge cases to cleaning, removing and replacing the spent primer, adding a measured amount of gun powder and seating a bullet in the neck of the cartridge case. Many firearm users conduct tests with particular rifles, particular types of cartridge cases, bullets and gun powder to develop a load that has extreme accuracy with that particular rifle.
When a cartridge chamber is grooved or fluted, the pressure of gun powder ignition will cause the cartridge case to be deformed into the grooves or flutes. This deformation often causes the cartridge cases to be un-useable for purposes of re-loading. A fluted cartridge chamber will also cause the debris of the burned gun powder to coat and foul the external surfaces of cartridge cases, sometimes to the point that the cartridge cases will be fouled and damaged such that re-loading becomes impossible or impractical. Therefore, it is desirable to provide a novel method and process for minimizing the force that is necessary for spent cartridge case extraction while ensuring that little or no cartridge gas pressure will be permitted to enter the cartridge chamber externally of the cartridge case upon firing of a cartridge. This feature prevents or significantly minimizes the presence of debris within the cartridge chamber and externally of the cartridge cases, and permits the spent cartridge cases to be extracted and ejected in a clean condition so that it may be simply and efficiently reloaded many times if desired.
Many autoloading firearm mechanisms employ a cartridge gas pressure responsive bolt mechanism which is driven rearwardly by cartridge gas pressure that is either applied directly to a bolt mechanism or is tapped from the barrel well forwardly of the cartridge chamber. Cartridge gas pressure entering from a port in the barrel will be applied to a piston and develop a piston force that achieves rearward movement of a bolt mechanism. As the bolt is moved rearwardly its extractor, being engaged with the rear rim of the cartridge that has been fired, will apply a rearward force to the cartridge rim, extracting the spent cartridge from the cartridge chamber. If the spent cartridge case is still in tight engagement with the internal support wall surfaces of the cartridge chamber, the extractor may not be able to extract the spent cartridge case. Under this condition the extractor can be pulled through the soft metal rim of the cartridge case, leaving the firearm inoperative until the spent cartridge case has been cleared from the cartridge chamber. The extractor may actually pull the rim portion of the cartridge case from the cartridge case body. This condition would also render the firearm inoperative until the remaining portion of the cartridge case has been cleared from the chamber. Therefore, it is desirable to provide a technology that minimizes the extraction force that is needed to extract a spent cartridge case without damaging it, even under circumstances where the cartridge case has not yet contracted to a normal condition for extraction after having been fired.
The longitudinal relieved areas are generated by removing by machining or by other processes, portions of the original reamed internal surface in the range of from about 0.0001″ to about 0.0010″ and constitute from about ⅔ to ¾ of the internal surface area of the tapered body support portion of the cartridge chamber while the longitudinal lands comprise about ⅓ to ¼ of the original internal surface area of the cartridge chamber. The neck portion of a cartridge case will establish an effective seal with the corresponding internal neck support surface of the cartridge chamber, thus preventing or substantially minimizing incursion of cartridge gas pressure between the cartridge case and the internal wall surface of the cartridge chamber.
A significant number of firearms have no cartridge case extraction mechanisms, but employ cartridge gas pressure to accomplish cartridge extraction from the cartridge chamber. When a cartridge is fired, its internal gas pressure acts both to propel the bullet from the cartridge case and to propel the cartridge case rearwardly. Typically, these types of firearms also employ cartridge gas pressure to overcome the mass of the bolt and the force of a bolt operating spring and propel the bolt of the firearm rearwardly. An ejector will then accomplish stripping of the spent cartridge case from the rearwardly moving bolt mechanism and will introduce a lateral force to eject the spent cartridge case from the receiver mechanism of the firearm. The bolt, after its rearward movement has ceased, will be driven forwardly by the bolt operating spring, retrieving a fresh cartridge from a magazine and moving the fresh cartridge into the cartridge chamber of the barrel in readiness for firing.
Both cartridge gas operated and recoil operated automatic and semi-automatic firearms have a common problem from the standpoint of bolt failure. When a cartridge is fired the cartridge case will instantly be driven rearwardly and will impart significant sharp and dynamic impact to the bolt mechanism. This sudden bolt thrust initiates bolt unlocking and rearward bolt movement and imparts significant stress to the bolt mechanism. The sudden bolt stress, which is repeated when each subsequent cartridge is fired, is a principal cause of early bolt failure. It is desirable, therefore, to provide a suitable means for introducing controlled impedance to cartridge case movement at the time of bullet launch, to thus minimize premature failure of the bolt mechanism.